Even after the shootings in the streets were done, police would discover more. The three bodies found in the alleged shooter's apartment. That's not all they found. ABC's Clayton Sandell tonight with more on that manifesto, as investigators try to peer into the mind of a killer. Clayton? Reporter: Good evening, David. Tonight, you can see some candles and flowers for the three men that police say Elliot Rodger killed inside his apartment complex here, but like so many things about this case, the victims were discovered only after this vie leaolent rampage ended. Tonight, so many clues in hindsight -- puzzle pieces put together too late. Elliot Rodger here. Reporter: Elliot Rodger left disturbing hints, starting with chilling youtube videos. I'll be a god. Exacting my retribution on all those that deserve it. Reporter: And with this 141-page manifesto detailing the troubled life of an alleged killer. From childhood bullying, sibiling rivalry, fantasies about killing his father and stepmother. And his most repeated grievance -- being rejected by women. Girls gave their affection and sex and love to other men, but never to me. I'm 22 years old and I'm still a virgin. He was really, really upset about, why is the world so unfair to him? And, oh, I'm a good-looking guy and why are girls going for the ugly fat guys? That's what he mentioned and I told him, appearance is not everything. Reporter: Rodger's family says their son was already being treated by multiple therapists. Nobody would do the types of things that happened last night unless there was some form of mental illness. Reporter: But because Rodger was never institutionalized for mental illness, it was legal for him to buy those three handguns along with hundreds of bullets. And his actions in the videos were so troubling, his parents alerted police. They went to his apartment less than a month before Friday's attack. The deputies contacted the suspect, at the time, found him to be polite and courteous. He downplayed the concerns for his welfare and the deputies cleared the call. Reporter: It's not clear if police could have done anything more. At an alarming rate, law enforcement are being asked to be law enforcers and psychiatric social workers. Reporter: But Rodger himself offered one clue. He wrote -- "If they had demanded to search my room, that would have ended everything." A lot of people seem to have some insight into Rodger's life, family, friends, therapists and police. But only one person, Elliot Rodger himself, seemed to have the whole picture. David? Clayton, thank you. Our coverage of the deadly rampage throughout the night at abcnews.com and, of course, first thing in the morning, right here on "Good morning America."

This transcript has been automatically generated and may not be 100% accurate.

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